The long-term objective of this project is to determine the multiple roles of mechanical forces in acute modulation of vascular tone, chronic remodeling of blood vessel walls, and localization of atherosclerotic plaques in regions of arterial curvature and branching. The fluid wall shear stress (WSS), driven by blood flow, and the solid circumferential strain (CS), driven by blood pressure, act simultaneously on the endothelial cells (ECs) lining blood vessel walls to modulate their biological activity. Blood flow can also limit oxygen transport to the wall at atherogenic sites which may lead to an increase in lipid permeation, a hallmark of atherosclerosis. In addition to blood flow forces on ECs, transmural flow driven by the transvascular pressure gradient imposes WSS on the smooth muscle cells (SMCs) in the arterial media. WSS on SMC can affect SMC contractile state, which in turn controls vascular tone, as well as SMC proliferation and migration rates which influence the progression of intimal hyperplasia and atherosclerosis. To determine the effects of these mechanical forces (WSS and CS) on vascular cells (ECs and SMCs) we will pursue the following specific aims: 1. To compute WSS, CS and oxygen transport in a model of the atherogenic carotid bifurcation. We will compute fluid flow and oxygen transport processes in a realistic 3-dimensional, elastic (moving wall) model of the carotid bifurcation under pulsatile flow conditions using a finite element code (FIDAP 8.5). We will compare spatial distributions of WSS, CS and oxygen flux to available distributions of intimal thickening in the human carotid bifurcation. 2. To simulate the fluid mechanical environment of the superficial SMC layers accounting for the complex entry conditions imposed by the internal elastic lamina (IEL). We will use FIDAP 8.5 to simulate fluid flow and mass transport processes in a realistic 3-dimensional model of the IEL and superficial layers of SMC. The unique mechanical environment of the SMCs at the intimal-medial boundary will be revealed. 3. To determine the effects of simultaneous CS and WSS over a range of dynamic conditions on EC biology. EC grown on the inner surface of elastic tubes will be exposed to combined CS and WSS over a broad range of phase angles in a unique apparatus. The effects of the mechanical environment on two classes of molecules will be determined: (1) vaso-reactive species: PGI2, NO, ET-1 and related mRNA: COX-2, eNOS and ET-1; (2) cell transport proteins: occludin and ZO-1 which regulates tight junction permeability, and connexin-43 which controls gap junctions. 4. To determine the effects of WSS on SMC contraction and migration. We will use a 2-dimensional model (SMC coated on a surface-treated quartz slide) and a 3-dimensional model (SMC suspended in a gel) to expose cells to controlled levels of WSS and will measure cell contraction and migration in response to these forces.